The present invention relates to a recording method in a facsimile receiver, and more particularly to a recording method in a facsimile receiver which is suitable for noise reduction, provides an improvement of the quality of the recorded image and makes possible recording of an image transmitted at a high rate.
The prior art recording methods in a facsimile receiver include a variable speed recording method in which the paper is fed by one line for each one line of image signals received from the receiver and a constant speed recording method in which one page of image signals are temporarily stored in a memory and the memory data is read out at a constant time interval and the paper is fed at a constant speed. In a high speed image recording, the former method requires a fast response drive motor for the paper feed. However, since there is a limit in the performance of the drive motor, the variable speed recording at higher than a certain limit is not attainable. Such a high performance motor also causes an increase in the size of the apparatus and the cost thereof. The latter method is suitable to high speed recording, but a memory of two-page capacity is required for the continuous recording. As a result, a large capacity memory is required and hence the cost increases.
The one line of image signals in the facsimile transmission is transmitted not periodically but at a random time interval. A minimum time interval (highest recording speed) is determined by the transmission capability of the communication line. The paper feed drive motor in the facsimile receiver must have an ability to follow a speed range varying from a low recording speed to the highest recording speed. However, a considerable time is usually required to accelerate the drive motor from its stop state to the highest recording speed. In the high speed facsimile, since the image signals are transmitted at a time interval shorter than the acceleration time, it is difficult to follow the speed change and a recording error results. A continuously variable speed sub-scan system has been proposed in which coded compressed information transmitted during a time period from the stop condition of the motor to the acceleration to the highest recording speed is stored in the buffer memory and a sub-scan rate is controlled by the number of coded bits in the buffer memory. In this system, however, since the number of lines stored in the buffer memory is unknown, line-by-line fine control is not attainable but a rough speed is instructed. In addition, the speed abruptly changes at the start or stop of recording and the quality of the image is degraded and noises and vibrations occur. Since a conventional transmitter includes the stop of recording, the communication is impeded.